1. Field of the Invention
The present invention relates to a buckle which engages with a tongue plate provided at a webbing of a seat belt device so as to maintain the webbing in an applied state.
2. Description of the Related Art
Conventional seat belt devices use a buckle which engages with a tongue plate so as to maintain a webbing in an applied state. The buckle includes, within a cover member, a buckle main body, a lock plate which engages with the tongue plate so as to be in a latched state, a release button which releases the latched state of the lock plate, an ejector which expels the tongue plate to the exterior by elastic force at the time the latch state is released, a lock pin for maintaining the latched state, and the like.
Simplification of the processes for manufacturing the buckle which is structured in this way is desired, and a reduction in the number of parts is desired from the standpoint of a reduction in costs.
Further, a mechanism which keeps the latched state of the lock plate to the tongue plate from being released even when an unplanned force is applied to the buckle is indispensable.
In view of the aforementioned, an object of the present invention is to provide a buckle in which the number of parts is reduced and which can reliably maintain a latched state.
A first aspect of the present invention is a buckle which engages with a tongue plate provided at a webbing in a seat belt device, comprising: a latch member engaging with the tongue plate which has been inserted to a predetermined position; a lock member abutting the latch member and maintaining an engaged state in which the latch member is engaged with the tongue plate; an operation member which, when operated, releases the lock member from the latch member; and a spring disposed between the operation member and the lock member, and urging the operation member to a pre-operation original position, and urging the lock member toward the latch member.
Operation of the first aspect will be described.
Due to the tongue plate being inserted in the buckle up to a predetermined position, the latch member engages the tongue plate so as to be in a latched state. At this time, the lock member, which is urged by the elastic force of the spring, abuts the latch member, and locks the latch member such that the latch member cannot be displaced from the engaged state. As a result, the latched state is maintained.
When the tongue plate is to be released from the buckle, by operating the operation member against the elastic force of the spring, the lock member separates from the latch member, and the locked state of the latch member is released. As a result, the engaged state of the latch member and the tongue plate is released, and the tongue plate is freed to the exterior, and the operation member is returned to its original position by the elastic force of the spring.
In this way, a single spring serves as both a spring for making the lock member abut the latch member and a spring for returning the operation member to its original position. Accordingly, the number of parts can be reduced, and the manufacturing process and assembly process can be simplified.
Further, because the latch member is locked by the lock member which is urged by the spring, the latched state is reliably maintained.
In a second aspect of the present invention, in the first aspect, the lock member is a freely rotating cam, and comprises: a first convex portion pushed in a lock releasing direction by operation of the operation member; and a second convex portion formed at a side of a center of rotation of the cam which is substantially opposite the side at which the first convex portion is disposed, an end of the spring engaging with the second convex portion, wherein a center of gravity of the cam is positioned toward the second convex portion.
Operation of the second aspect will be described.
When the latch member engages the tongue plate which has been inserted in the buckle up to a predetermined position (i.e., when the latched state is set), the lock member (cam) urged by the spring rotates, and the lock member (the second convex portion) abuts the latch member. As a result, the latch member is locked, and the latched state is maintained.
When the latched state is to be released, by operating the operation member, the first convex portion is pressed, and the lock member rotates in the lock releasing direction. As a result, the lock member separates from the latch member, and the locked state is released. As a result, the engaged (latched) state of the latch member and the tongue plate is released.
At this time, the operation member is returned to its original position due to the urging force of the spring.
The implementing and releasing of the latched state are carried out in this way. However, when an impact force in the lock releasing direction acts on the buckle, because the first convex portion and the second convex portion are disposed at substantially opposite sides of the center of rotation of the cam, rotational moments in opposite directions (the lock releasing direction and the direction opposite thereto) act on the first convex portion and the second convex portion. However, because the center of gravity of the lock member (cam) is positioned toward the second convex portion side, a rotational moment in the direction opposite to the lock releasing direction acts on the lock member. Accordingly, the latched state (locked state) of the buckle is not released due to the impact force, and is reliably maintained.